Stabilizer mixture of chroman derivatives and inert organic solvents, and microcapsules containing this stabilizer mixture

ABSTRACT

PCT No. PCT/EP96/00058 Sec. 371 Date Jul. 16, 1997 Sec. 102(e) Date Jul. 16, 1997 PCT Filed Jan. 9, 1996 PCT Pub. No. WO96/22325 PCT Pub. Date Jul. 25, 1996The stabilizer mixture comprises (a) one or more chroman derivatives of the formula I    &lt;IMAGE&gt;  (I)  where R1 is   &lt;IMAGE&gt;    &lt;IMAGE&gt;   in which Z is C7- to C30-alkyl, -CH2CH2-S-(C1- to C30-alkyl) or   &lt;IMAGE&gt;   and (b) an inert organic solvent for the chroman derivatives I from the group consisting of aliphatic, cycloaliphatic or aromatic hydrocarbons or halogenated hydrocarbons, silicone oils and vegetable and animal fats, where components (a) and (b) are in a weight ratio of from 99:1 to 1:99.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel stabilizer mixture of chromanderivatives and inert organic solvents which may additionally containorganic phosphites or phosphonites and/or amines, for stabilizingorganic material against the action of light, oxygen and in particularheat. The invention furthermore relates to microcapsules containing thisstabilizer mixture of chroman derivatives and inert organic solventsand, if desired, organic phosphites or phosphonites and/or amines, whichmicrocapsules can likewise be used for stabilizing organic materialagainst the action of light, oxygen and in particular heat.

2. Description of the Related Art

DE-A 36 34 531 (1) discloses stabilizer mixtures of chroman derivatives(vitamin E, α-tocopherol) and organic phosphites or phosphonites forstabilizing plastics. However, the mixtures have the disadvantage ofbeing unstable both during storage and after incorporation into theplastics. A decrease in the chroman derivative content, probably owingto hydrolysis reactions in the presence of traces of atmosphericmoisture, and thus a reduction in the stabilizing action on the plasticsis observed.

German Patent Application P 44 05 670.2 (2) recommends a stabilizermixture of chroman derivatives, organic phosphites or phosphonites andamines for stabilizing organic material, in particular plastics, butthis mixture likewise has inadequate stability during incorporation intothe plastics.

The above stabilizer mixtures of the prior art furthermore have themajor disadvantage of being liquids or pastes and thus being extremelydifficult to mix with thermoplastics. Most plastics manufacturers andprocessors are furthermore unable to meter such additives in liquid formand require solid additives, which are readily weighable and easy tohandle and admix.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a stable stabilizermixture which can be used in the form of a solid.

We have found that this object is achieved by a stabilizer mixture whichcomprises

(a) one or more chroman derivatives of the formula I ##STR4## where R¹is ##STR5## in which Z is C7- to C₃₀ -alkyl, preferably C₁₃ - to C₁₉-alkyl,

--CH₂ CH₂ --S--(C₁ - to C₃₀ -alkyl), preferably --CH₂ CH₂ --S--(C₈ - toC₂₀ -alkyl), or ##STR6## and (b) an inert organic solvent for thechroman derivatives I from the group consisting of aliphatic,cycloaliphatic or aromatic hydrocarbons or halogenated hydrocarbons,silicone oils and vegetable and animal fats,

where components (a) and (b) are in a weight ratio of from 99:1 to 1:99,preferably from 90:10 to 5:95, in particular from 60:40 to 10:90.

DETAILED DESCRIPTION OF THE INVENTION

Suitable chroman derivatives I are in particular2,5,7,8-tetra-methyl-2-(2'-stearoyloxyethyl)chroman (R¹ =--CH₂ CH₂--O--CO--C₁₇ H₃₅) and especially α-tocopherols, preferablyDL-α-tocopherol (R¹ =--(CH₂)₃ --CH(CH₃)--(CH₂)₃ --CH(CH₃)-(CH₂)₃--C(CH₃)₂)

Particularly suitable inert organic solvents (b) for the chromanderivatives I are

benzine, mineral oil and paraffins, such as white oil

partially hydrogenated terphenyls

toluene, xylenes and C₂ - to C₁₈ -alkylbenzenes, such as dodecylbenzene

C₁ - to C₁₂ -alkylnaphthalenes

chlorinated paraffins

fluorocarbons

conventional polysiloxanes, such as polydimethylsiloxane orpoly(methylphenylsiloxanes)

naturally occurring triglycerides of saturated and/or unsaturated fattyacids, such as soybean oil, colza oil, olive oil, sunflower oil,cottonseed oil, groundnut oil, linseed oil, rapeseed oil or fish oil.

These inert organic solvents (b) are normally heat-resistant at theusual temperatures at which additives are incorporated into plastics,ie. up to about 300° C. They generally have low volatility and have, inparticular, boiling points of above 80° C.

The organic solvents (b) can also be employed in the form of mixtures ofmore than one of said species.

The novel stabilizer mixture may additionally comprise

(c) one or more organic phosphites of the formula II ##STR7## where R²to R⁴ are each C₂ - to C₁₂ -alkyl, preferably C₆ - to C₁₁ -alkyl, inparticular C₈ - to C₁₀ -alkyl, or C₆ - to C₁₈ -aryl, preferably phenyl,which may be substituted by C₁ - to C₁₈ -alkyl groups, preferably by oneto three C₄ - to C₁₂ -alkyl groups,

or an organic phosphonite of the formula III ##STR8## or a mixture of aphosphite II and a phosphonite III, and/or (d) one or more amines of theformula IV ##STR9## where R⁵ to R⁷ are each hydrogen, C₁ - to C₁₈-alkyl, which may be interrupted by up to 5 non-adjacent oxygen atoms orgroups of the formula --NR⁸ -- and may be substituted by up to 3hydroxyl groups, where R⁸ is hydrogen or C₁ - to C₄ -alkyl, or arephenyl which may be up to trisubstituted by C₄ - to C₁₈ -alkyl, butwhere the amine IV is not NH₃,

where components (b) and (c) are in a weight ratio of from 100:0 to1:99, and component (d) is present in the stabilizer mixture in anamount of from 0 to 2.0% by weight, based on the amount of (a)+(c).

It is thus possible for the stabilizer mixtures to comprise components(a)+(b), (a)+(b)+(c), (a)+(b)+(d) or (a)+(b)+(c)+(d) as essentialconstituents. If (c) is present, the (b):(c) weight ratio is preferablyfrom 95:5 to 5:95; it has proven favorable for the (a):(c) weight ratiosimultaneously to be in a range from 1:1 to 1:14, in particular from 1:5to 1:10. If (d) is present, this component is preferably present in thenovel stabilizer mixture in an amount of from 0.001 to 2.0% by weight,in particular from 0.01 to 1.0% by weight, especially from 0.02 to 0.5%by weight, in each case based on the amount of (a)+(c).

The organic phosphites II which can be employed are either liquid orcrystalline products. Examples of such phosphites which may be mentionedare the following:

trisalkyl phosphites, preferably containing long-chain linear orbranched alkyl groups, such as octyl, nonyl, isononyl, decyl or isodecylgroups;

trisaryl phosphites containing unsubstituted or mono- totrialkyl-substituted aryl groups, such as phenyl, nonylphenyl or2,4-di-tert-butylphenyl groups;

mixed aryl alkyl phosphites, such as diisodecyl phenyl phosphite ordiphenyl pentaerythrityl diphosphite.

The phosphites of the formula II can be synthesized by known methods,for example by reacting PCl₃ with monohydric or polyhydric alcohols inthe presence of an organic base or with substituted or unsubstitutedphenols, with or without solvents, at from 20° to 250° C. The mixedalkyl aryl phosphites are prepared, for example, by reacting triphenylphosphite with monohydric or polyhydric alcohols in the presence of abasic catalyst, preferably without solvents.

The phosphonite III is known and is commercially available as Irgafos®P-EPQ from Ciba-Geigy.

Suitable amines IV are primary, secondary or preferably tertiary amines.

Examples of such amines which may be mentioned are butylamine,dibutylamine, tributylamine, tripropylamine, triisopropylamine,octylamine, diisobutylamine and stearylamine.

Preference is furthermore given to amines in which R⁵ to R⁷ arehydroxyl-containing radicals having 2 to 18 carbon atoms, for exampleethanolamine, diethanolamine, triethanolamine, propanolamine,dipropanolamine, tripropanolamine, isopropanolamine, diisopropanolamineand in particular triisopropanolamine.

However, the amines IV should not have excessively high volatility,which means that ammonia (NH₃) is unsuitable for the novel stabilizermixture.

The novel stabilizer mixture is highly suitable for stabilizing organicmaterial against the action of light, oxygen and in particular heat. Itis also effective as a metal deactivator. It is added to the organicmaterial to be stabilized, before, during or after the preparationthereof, in a concentration of from 0.005 to 5.0% by weight, preferablyfrom 0.01 to 2.0% by weight, in particular from 0.05 to 1.0% by weight,based on the organic material.

The novel stabilizer mixture is furthermore not only an excellentantioxidant, in particular for plastics, but also an effectivedispersant for pigments in liquid paints.

Examples of organic materials are cosmetic preparations, such asointments and lotions, medicament formulations, such as pills andsuppositories, photographic recording materials, in particularphotographic emulsions, precursors for plastics and paints, or paintsthemselves, but in particular plastics themselves.

This invention therefore also relates to organic material, in particularplastic, which is stabilized against the action of light, oxygen and inparticular heat and contains the novel stabilizer mixture in theabovementioned concentrations.

The novel stabilizer mixture can be mixed, in particular, with plasticsusing all known equipment and methods for mixing stabilizers or otheradditives with polymers.

The novel stabilizer mixture can be used, in particular, for stabilizingplastics during their processing. Stabilizer mixtures of this type areadded to plastics during or before processing in order to protect theplastics against decomposition, it being possible, as is known, for theeffects of various stabilizer systems to supplement one another.

In addition to the novel stabilizer system comprising components (a),(b) and, if desired, (c) and/or (d), further stabilizer additives, forexample the synergists calcium stearate and distearyl thiodipropionate(S--(CH₂ CH₂ --COOC₁₈ H₃₇)₂) known for stabilization purposes, can alsobe mixed with the plastics in conventional amounts.

It is also possible to prepare concentrates of the stabilizers describedtogether with plastics and then to process these together with theplastics to be stabilized. Depending on the area of application,concentrates have advantages during processing, since they are easier tohandle and meter.

The following are examples of plastics which can be stabilized by thenovel stabilizer mixture:

polymers of mono- and diolefins, for example low-density or high-densitypolyethylene, polypropylene, linear poly-1-butene, polyisoprene,polybutadiene and copolymers of mono- or diolefins or mixtures of saidpolymers;

polystyrene and copolymers of styrene or a-methylstyrene with dienesand/or acrylate derivatives, for example styrene-butadiene,styrene-acrylonitrile (SAN), styrene-ethyl methacrylate,styrene-butadiene-ethyl acrylate, styrene-acrylo-nitrile-methacrylate,acrylonitrile-butadiene-styrene (ABS) or methylmethacrylate-butadiene-styrene (MBS);

halogen-containing polymers, for example polyvinyl chloride, polyvinylfluoride, polyvinylidene fluoride and copolymers thereof;

polymers derived from α,β-unsaturated acids and derivatives thereof,such as polyacrylates, polymethacrylates, polyacrylamides andpolyacrylonitriles;

polymers derived from unsaturated alcohols and amines or from theiracrylic derivatives or acetals, for example polyvinyl alcohol andpolyvinyl acetate;

polyurethanes, polyamides, polyureas, polyphenylene ethers, polyesters,polycarbonates, polysulfones, polyether sulfones and polyether ketones.

Readily stabilizable plastics are, in particular, thermoplastics, suchas polyvinyl chloride, styrene polymers, polyamides, polycarbonates,polyphenylene oxide, polyesters, polyolefins, preferably polyethyleneand polypropylene, polyurethanes and thermosets.

In addition to the low inherent color and the processing stability,factors of particular importance for the suitability and effectivenessof the novel stabilizer mixture are, in particular, the hydrolysis andthe stable content of chroman derivatives I.

The present invention furthermore relates to microcapsules containingthe novel stabilizer mixture of components (a), (b) and, if used, (c)and/or (d).

The wall material (shells) of these microcapsules are usually solidpolymeric materials of natural or preferably synthetic origin,containing, in the core, the novel stabilizer mixture in liquid orsuspension form, which mixture generally makes up from 50 to 95% byweight, in particular from 70 to 90% by weight, of the total weight ofthe microcapsules.

The prior art includes microcapsules whose walls comprisepolycondensates based on urea, phenol or in particular melamin andformaldehyde. For example, EP-B 026 914 (3) discloses a process for theproduction of such microcapsules by condensation of melamin-formaldehydeprecondensates or C₁ - to C₄ -alkyl ethers thereof in water in which thewater-insoluble material formed in the capsule core is dispersed, in thepresence of dissolved polymers containing negatively charged ionicgroups, in particular sulfo-containing polymers. The microcapsulesobtainable in this way are employed for the production ofpressure-sensitive recording papers. The microcapsule production processdescribed in (3) is likewise highly suitable for the production of thenovel microcapsules containing the stabilizer mixture of components (a),(b) and, if used, (c) and/or (d).

Suitable starting substances for the wall material are preferablymelamin-formaldehyde precondensates and C₁ - to C₄ -alkyl ethersthereof, preferably with a melamin:formaldehyde weight ratio of from 1:3to 1:6. These precondensates are N-methylolmelamin compounds or ethersthereof with alkanols. The precondensates used for the process should beinfinitely miscible with water without forming turbidity. It must bepossible for any turbidity formed as a result of cooling to be removedby warming. For these reasons, ethers of methylolmelamins areparticularly preferred.

Suitable water-soluble, sulfo-carrying polymers can be, for example,homopolymers or copolymers or sulfoethyl (meth)acrylates, of sulfopropyl(meth)acrylates, of maleimido-N-ethanesulfonic acid or of2-acrylamido-2-methylpropanesulfonic acid. Preference is given topolymers of 2-acrylamido-2-methylpropanesulfonic acid, which can easilybe polymerized to give polymers having the desired K values. Thepolymers are in the form of the free acid or preferably in the form ofthe alkali metal or trisubstituted ammonium salts. Other suitablesulfo-carrying polymers are copolymers built up from said sulfo-carryingmonomers or vinyl-sulfonic acid and C₁ - to C₃ -alkyl acrylates,hydroxy-C₂ - to C₄ -alkyl acrylates, such as methyl, ethyl, n- orisopropyl acrylate, hydroxypropyl acrylate and/or N-vinylpyrrolidone. Inthe case of the acrylates, their maximum proportion in the copolymer is30% by weight. In the case of the hydroxyalkyl acrylates, theirproportion should not be greater than 10% by weight, based on the totalamount of the comonomers. In the case of copolymers withN-vinylpyrrolidone the proportion of sulfo-carrying monomers is at least5% by weight, preferably 30% by weight or above, based on the totalamount of the comonomers. Of the copolymers, preference is given tothose with 2-acryl-amido-2-methylpropanesulfonic acid as sulfo-carryingcomonomers. The sulfo-carrying homopolymers and copolymers are preparedby known processes.

The polymers should have a Fikentscher K value of from 100 to 170(measured in 1% strength by weight aqueous solution at 20° C.) or aviscosity of from 200 to 5000 mPas at a shear gradient of 489 s⁻¹(measured at 25° C. in 20% strength by weight aqueous solution at pH 4.0to 7.0). Preference is given to polymers having a K value of from 115 to160 with a viscosity of from 400 to 4000 mPas.

The amount of water-soluble, sulfo-containing polymers is generally from1 to 5.5% by weight, preferably from 1.5 to 4.5% by weight, based on theaqueous phase.

The optimum amount of water-soluble, sulfo-containing polymers isdetermined firstly by the polymer itself, and secondly by the reactiontemperature, the microcapsule size desired and the melamin-formaldehydeprecondensate. The optimum amount can easily be determined by simpleexperiments. It has been found that the optimum concentration of thewater-soluble, sulfo-containing polymers is virtually independent of theratio between the aqueous, continuous phase and the organic,water-insoluble core material phase. This means that, once theconditions have been optimized, microcapsule dispersions having variablecontents of capsules can be produced with virtually constant quality.

The condensation of the precondensates during and after the capsuleformation is expediently continued and completed at a pH of from 3.0 to6.5, preferably from 3.5 to 5.5. The pH in the aqueous phase can be setusing acids, such as sulfuric acid, hydrochloric acid, nitric acid,phosphoric acid, oxalic acid or preferably formic acid, or, if theaqueous phase is acidic, using sodium hydroxide solution. Thecommencement of turbidity, ie. precipitation of the melamin-formaldehydecondensate, is somewhat dependent on the precondensate, though theoptimum pH values and temperatures vary somewhat for the formation ofmicrocapsules from various precondensates.

In general, temperatures of from 15° to 100° C. are expedient for theprocess described; temperatures of from 40° to 90° C. are preferred inorder to achieve faster microcapsule formation.

The condensation of the precondensate can be continued in the region ofthe above pH values and temperatures, in the absence or alternatively inthe presence of the water-soluble, sulfo-carrying high polymers. Thelatter process is preferred, since the condensate particles whichprecipitate from the aqueous solution, causing the turbidity, are thenof more uniform size.

The hydrophobic material to be encapsulated, ie. the novel stabilizermixture, can either be added after the appearance of the turbidity orcan already be present during further condensation of the precondensate.

The process described allows the production of microcapsules of variousdiameter. Thus, the capsules are generally smaller if more precondensateor hydrophilic protective colloid (ie. the sulfo-containing polymers) isemployed or if dispersal is more intensive or if the residence time inthe dispersion step is extended. Larger capsules are obtainedcorrespondingly with the converse measures, individually or incombination. The degree of further condensation of the precondensateaffects the capsule size. The smallest capsules are obtained at itsoptimum under otherwise constant conditions. In general, capsules havingdiameters of from 1 to 200 μm, in particular from 2 to 50 μm, areobtained.

The microencapsulation is generally carried out batchwise as describedin (3). However, it can also be carried out continuously, for example asdescribed in EP-B 218 887 (4).

The formaldehyde liberated during the condensation of themelamin-formaldehyde precondensates can be bound, for example in a knownmanner using ammonia at a pH above from 7 to 8 or using urea orethyleneurea. It is particularly advantageous to bind the freeformaldehyde in resultant dispersions by condensation with melamin. Tothis end, the particle dispersion, which is still acidic as aconsequence of the condensation, is mixed continuously with a suspensionof melamin in water (melamin:water weight ratio preferably from 1:2 to1:4) with stirring for a course of from 30 minutes to 2 hours at from60° to 90° C., preferably at from 70° to 85° C., and at a pH of from 4.0to 5.0, the condensation being continued until the free formaldehyde hasbeen consumed.

The dispersions obtained by the process can be dried, for example in aspray drier. The resultant powders are free from agglomerates and caneasily be incorporated into water or solvent containing systems. Forisolation by spray drying, dispersions which have been completely freedfrom precondensate are particularly suitable.

Besides the melamin resin process described above, other processes canbe employed to prepare the novel microcapsules, for example theprocesses of EP-A 457 154 (5) using C₁ - to C₂₄ -alkyl esters of acrylicor methacrylic acid, of EP-A 468 323 (6) by interfacial polyaddition orinterfacial polycondensation between a hydroxylamine and a componentwhich is reacted with amino and alcohol groups, for example isocyanate,or of U.S. Pat. No. 5,064,470 (7) using gelatin, for example incombination with gum arabic.

Pulverulent microcapsules are particularly suitable for incorporationinto a plastic as a readily meterable solid with the aid of an extruder.In this way, the novel stabilizer mixtures in the form of driedmicrocapsule dispersions can be homogeneously premixed with plasticgranules and processed in the extruder without caking or other machineproblems.

Just like the novel stabilizer mixture itself, the novel microcapsulesare highly suitable for stabilizing organic material, in particularplastics, against the action of light, oxygen and in particular heat anddo not loose their effectiveness due to the microencapsulation. They arealso effective as metal deactivators. They are added to the organicmaterial to be stabilized before or during its preparation, in aconcentration of from 0.005 to 10.0% by weight, preferably from 0.01 to4.0% by weight, in particular from 0.05 to 2.0% by weight, based on theorganic material.

The present invention also relates to organic material, in particularplastics, which has been stabilized against the action of light, oxygenand in particular heat and contains the novel microcapsules in theconcentrations given above.

With respect to the definition of organic material, the manner andpurpose of incorporation into plastics and the choice of plastics whichcan be stabilized, refer to the above comments.

The process described for the production of the novel microcapsules isillustrated in greater detail by the working examples below.Hereinafter, parts and percentages are by weight. The percentages arethemselves based on the weight of the solution or dispersion. Parts byvolume correspond to parts by weight with density 1.

The solids content given in the examples was determined by drying (4hours at 105° C.) and essentially comprises the microcapsules and thewater-soluble polymer. The screen residue was obtained by screening thedispersion through a vibrating screen with a mesh width of 40 μm and wasweighed while moist. It then contained about 50% water. The capsulediameters were determined subjectively under a microscope andobjectively by means of a Malvern Autosizer. The capsule diameter isgiven for the most frequent particle size (number average) and for theparticle fraction having the greatest total volume (volume average) andthe half value width of the volume average as the capsule diameter orthe capsule diameter difference (HW) found at 50% of the frequency inthe differential distrubition curve.

The viscosity of the capsule dispersion is given as the efflux time inseconds of a 100 ml dispersion from a DIN cup with 4 mm nozzle. Theviscosity of the 20% strength solutions of the water-soluble polymerscontaining highly acidic groups, for example sulfo groups, was measuredat 25° C. in a Rheomat® 30 (Contraves) at a shear gradient of 489 sec⁻¹.The Fikentscher K value (Cellulosechemie 13 (1932), 58 ff.) wasdetermined on a 1% strength solution in water at 20° C.

EXAMPLE 1

1000 g of water, 141 g of a 70% strength aqueous solution of a partiallymethylated precondensate (containing approx. 2.3 CH₃ O groups permelamin molecule) of 1 mol of melamin and 5.25 mol of formaldehyde whichforms a clear solution in water, and 129 g of a 20% strength aqueoussolution of poly(sodium 2-acrylamido-2-methylpropanesulfonate) (Kvalue=140) were introduced into a cylindrical 4 l stirred reactor fittedwith dissolver stirrer with 5 cm disk. A solution of 93 g ofDL-α-tocopherol in 618 g of white oil was added and dispersed at 30° C.at a stirrer speed of 3000 rpm. The pH was adjusted to 3.6 using formicacid. After dispersal for 1 hour, the batch was stirred for a furtherhour at 30° C. using a propeller stirrer at 800 rpm. The mixture wasthen heated to 80° C. with stirring and kept at this temperature for 2hours. The microcapsule dispersion was then neutralized to a pH of 7.5using a 50% strength solution of triethanolamine in water.

The microcapsules had a particle size of from 8 to 20 μm when observedby light microscopy. The solids content of the dispersion was 39.4%.2000 g of the dispersion were dried in a spray drier at an inlettemperature of 140° C. and an outlet temperature of 65°-70° C. The yieldwas 807 g of a free-flowing powder having a solids content of 95.7%.

EXAMPLE 2

1100 g of water, 158 g of a 70% strength aqueous solution of a partiallymethylated precondensate (containing approx. 2.3 CH₃ O groups permelamin molecule) of 1 mol of melamin and 5.25 mol of formaldehyde whichforms a clear solution in water, and 145 g of a 20% strength aqueoussolution of poly(sodium) 2-acrylamido-2-methylpropanesulfonate) (Kvalue=140) were introduced into a cylindrical 4 l stirred reactor fittedwith dissolver stirrer with 5 cm disk. A solution of 398 g ofDL-α-tocopherol in 398 g of white oil was added and dispersed at 30° C.at a stirrer speed of 3000 rpm. The pH was adjusted to 3.6 using formicacid. After dispersal for 1 hour, the batch was stirred for a furtherhour at 30° C. using a propeller stirrer at 800 rpm. The mixture wasthen heated to 80° C. with stirring and kept at this temperature for 2hours. The microcapsule dispersion was then neutralized to a pH of 7.5using a 50% strength solution of triethanolamine in water.

The microcapsules had a particle size of from 7 to 20 μm when observedby light microscopy. The Malvern Autosizer gave a result of D(10)=2.8μm, D(50)=16.3 μm, D(90)=30.9 μm and a volume average value D(4.3)=17.0μm. The solids content of the dispersion was 39.5%. 2150 g of thedispersion were dried in a spray drier at an inlet temperature of 140°C. and an outlet temperature of 65°-70° C. The yield was 890 g of afree-flowing powder having a solids content of 95.7%.

EXAMPLE 3

1000 g of water, 141 g of a 70% strength aqueous solution of a partiallymethylated precondensate (containing approx. 2.3 CH₃ O groups permelamin molecule) of 1 mol of melamin and 5.25 mol of formaldehyde whichforms a clear solution in water, and 129 g of a 20% strength aqueoussolution of poly(sodium) 2-acrylamido-2-methylpropanesulfonate) (Kvalue=140) were introduced into a cylindrical 4 l stirred reactor fittedwith dissolver stirrer with 5 cm disk. A solution of 93 g ofDL-a-tocopherol and 93 g of trisnonylphenyl phosphite in 525 g of whiteoil was added and dispersed at 30° C. at a stirrer speed of 3000 rpm.The pH was adjusted to 3.6 using formic acid. After dispersal for 1hour, the batch was stirred for a further hour at 30° C. using apropeller stirrer at 800 rpm. The mixture was then heated to 80° C. withstirring and kept at this temperature for 2 hours. The microcapsuledispersion was then neutralized to a pH of 7.5 using a 50% strengthsolution of triethanolamine in water.

The microcapsules had a particle size of from 7 to 20 μm when observedby light microscopy. The solids content of the dispersion was 39.5%.2000 g of the dispersion were dried in a spray drier at an inlettemperature of 140° C. and an outlet temperature of 65°-70° C. The yieldwas 800 g of a free-flowing powder having a solids content of 96.7%.

Use Example

The most important factor for the suitability and effectiveness ofplastic stabilizers is the processing stability.

The microencapsulated stabilizer mixtures from Examples 1 to 3 werehomogenized in additive-free, dechlorinated polypropylene in an extruderand granulated. The melt flow index of this sample after extrusion oncewas determined in accordance with DIN 53 735. This sample was thenextruded a further four times and granulated, and the melt flow index ofthe extrudate was determined after the third and fifth extrusions.

The results are shown in the table below. The quality of the extrudedplastic is better the lower the melt flow index.

                  TABLE                                                           ______________________________________                                                                   Melt flow                                                      Concentration of the                                                                         index after                                        Stabilizer  stabilizer mixture in the                                                                    the                                                mixture from                                                                              polypropylene  1st    3rd 5th                                     Example No.  % by weight!  Extrusion                                          ______________________________________                                        1           0.10           26     33  46                                      2           0.03           27     35  48                                      3           0.10           25     32  45                                      For comparison:                                                                           --             39     77  >150                                    no stabilizer                                                                 ______________________________________                                    

We claim:
 1. A microcapsule, comprising:a stabilizer mixturecomprising(a) one or more chroman derivatives of the formula I ##STR10##where R¹ is ##STR11## in which Z is C₇ - to C₃₀ -alkyl --CH₂ CH₂--S--(C₁ - to C₃₀ -alkyl) or ##STR12## and (b) an inert organic solventfor the chroman derivatives I selected from the group consisting ofaliphatic hydrocarbons, cycloaliphatic hydrocarbons, aromatichydrocarbons, halogenated hydrocarbons, silicone oils, vegetable fats,and animal fats,where components (a) and (b) are in a weight ratio offrom 99:1 to 1:99.
 2. The microcapsule as claimed in claim 5, whichadditionally comprises(c) one or more organic phosphites of the formulaII ##STR13## where R² to R⁴ are each C₂ - to C₁₂ -alkyl or C₆ - to C₁₈-aryl which may be substituted by C₁ - to C₁₈ -alkyl,or an organicphosphonite of the formula III ##STR14## or a mixture of a phosphite IIand a phosphonite III, and/or (d) one or more amines of the formula IV##STR15## where R⁵ to R⁷ are each hydrogen, C₁ - to C₁₈ -alkyl which maybe interrupted by up to 5 non-adjacent oxygen atoms or groups of theformula --NR⁸ -- and may be substituted by up to 3 hydroxyl groups,where R⁸ is hydrogen or C₁ - to C₄ -alkyl, or are phenyl which may be upto trisubstituted by C₄ - to C₁₈ -alkyl, but where the amine IV is notNH₃,where components (b) and (c) are in a weight ratio of from 100:0 to1:99, and component (d) is present in the stabilizer mixture in anamount of from 0 to 2.0% by weight, based on the amount of (a)+(c). 3.An organic material which has been stabilized against the action oflight, oxygen and heat, comprising from 0.005 to 5.0% by weight, basedon the amount of the organic material, of the microcapsule as claimed inclaim
 1. 4. An organic material which has been stabilized against theaction of light, oxygen and heat, comprising from 0.005 to 10.0% byweight, based on the amount of the organic material, of the microcapsuleas claimed in claim
 1. 5. A method of stabilizing an organic materialagainst the action of light, oxygen and/or heat, comprising combining anorganic material with the microcapsule as claimed in claim
 5. 6. Amethod of stabilizing an organic material against the action of light,oxygen and/or heat, comprising combining an organic material with themicrocapsule as claimed in claim
 2. 7. A method of stabilizing anorganic material against the action of light, oxygen and/or heat,comprising combining an organic material with the microcapsule of claim5.
 8. A method of stabilizing an organic material against the action oflight, oxygen and/or heat, comprising combining an organic material withthe micro capsule of claim
 10. 9. The microcapsule as claimed in claim1, wherein said microcapsule comprises a polymeric shell and a core,wherein said stabilizer mixture is present in said core.
 10. Themicrocapsule as claimed in claim 1, wherein said stabilizer mixture ispresent in said microcapsule in liquid or suspension form.
 11. Themicrocapsule as claimed in claim 1, wherein said stabilizer mixture ispresent in an amount of 50-95% by weight, based on the total weight ofsaid microcapsule.
 12. The microcapsule as claimed in claim 11, whereinsaid stabilizer mixture is present in an amount of 70-95% by weight,based on the total weight of said microcapsule.
 13. The microcapsule asclaimed in claim 9, wherein said shell comprises at least onepolycondensate polymer comprised of a monomer selected from the groupconsisting of urea, phenol, melamine, and formaldehyde, and mixturesthereof.